1. Field of the Invention
The present invention pertains generally to infrared thermometers and more specifically, to an improved infrared thermometer apparatus including means for making more accurate temperature measurements by providing an observable indication of the precise field of view of the infrared radiation upon which the temperature measurement is based.
2. Prior Art
It is well-known in the art to utilize infrared thermometers. Such temperature measuring devices are used in measuring the temperature of an object or a series of closely spaced adjacent objects by measuring the relative infrared radiation levels using an infrared detector such as a thermopile. In these devices it is typical for a circuit to be used to convert the signal produced by the infrared detector and associated circuitry such as, for example, an amplifier and a linearization circuit, into an output signal capable of indicating a numerical value. This output signal is then utilized in a meter type structure such as a digital display or a known meter movement in order to indicate a numerical temperature value. Exemplary of such prior art devices are those disclosed in U.S. Pat. Nos. 4,078,179; 4,132,902 and 4,301,682, all issued to the applicant of the present invention.
The technology of infrared thermometry has matured to the point at which currently available infrared thermometers can provide an accuracy of 0.5 degrees centigrade over a temperature range of from -30 degrees centigrade to +100 degrees centigrade. In addition, infrared thermometers can now accurately measure the temperature of objects located at any distance from as near as one inch from the instrument to as far as 1000 feet or more from the instrument as long as the object completely fills the instrument's field of view. It is therefore, highly desirable for a user of a infrared thermometer to be able to discern the outline of the intersection of the infrared field of view with the body of which the temperature is being measured by the infrared thermometer.
Discerning the outline of this intersection is important in some applications even when it is clearly obvious that the object completely fills the instrument's field of view. By way of example, there may be occasions when it is desirable to measure the temperature of a specific portion of a larger object such as a particular leaf or stem of a plant in agricultural applications or on the forehead of a patient in medical applications. In this latter example it is particularly desirable to be able to observe the intersection of a field of view of the infrared detector and a selected portion of a patient when the instrument is being used to measure the patient's temperature from any substantial distance to the patient as may be the case when an infrared thermometer is used to spot check the forehead temperatures of sleeping infants in a hospital nursery.
Providing a user with the opportunity to observe the cross-section of the field of view of the infrared detector with an object is particularly advantageous during temperature measurements being made at distances substantially exceeding the focal length of the infrared optics which is normally in the range of about 2 to 4 inches where it provides means for viewing both the cross-section field of view as well as the temperature reading concurrently. This latter feature is particularly important in a portable hand-held infrared temperature apparatus where it is quite likely that the instrument will be moved over the period between observation of the field of view cross-section and observation of the temperature measurement. Those having skill in the art to which the present invention pertains will understand that even the slightest inadvertent motion of the infrared thermometer, particularly at measurement distances greater than several feet, will significantly change the position of the field of view cross-section relative to the object and may therefore result in gross inaccuracies in the temperature measurement.
There have been some attempts made in the prior art to provide portable hand-held infrared thermometers which provide some means for pointing the instrument at a particular location to enhance the accuracy of the temperature measurement. By way of example, Raytek Incorporated of Mountain View, Calif. provides a hand-held infrared thermometer designated RAYNGER II which provides a sighting telescope which permits the user to point the instrument at a precise location designated by the cross-hairs in the telescope. However, this prior art instrument does not provide the user with any accurate observation of the actual outline of the field of view intersection with the object being measured, nor does it solve the aforementioned problem of inadvertent hand motion between observation through the telescope and observation of the temperature measurement. In other prior art devices a source of light such as a small incandescent light bulb is provided at the front of the instrument and creates a beam of light that can be of some assistance in positioning the infrared field of view relative to an object at or near the focal point of the infrared optics. However, the beam of light becomes relatively indiscernible at distances exceeding the focal length of the optics and in addition, presents the danger of substantially reducing the accuracy of the temperature measurement process by introducing a source of high temperature (the incandescent lamp) that is located near the infrared detector. Finally, such prior art devices that use a bare incandescent lamp as a pointing indicator which only operates favorably at or near the focal point of the infrared optics, render it virtually impossible to monitor the position of the light beam on an object while simultaneously reading the temperature measurement. Consequently, the aforementioned prior art disadvantage with respect to inadvertent movement of a hand-held portable infrared thermometer is likely to still be a problem.